Light emitting device having a pluralilty of light emitting cells and package mounting the same

ABSTRACT

Disclosed is a light emitting device having a plurality of light emitting cells and a package having the same mounted thereon. The light emitting device includes a plurality of light emitting cells which are formed on a substrate and each of which has an N-type semiconductor layer and a P-type semiconductor layer located on a portion of the N-type semiconductor layer. The plurality of light emitting cells are bonded to a submount substrate. Accordingly, heat generated from the light emitting cells can be easily dissipated, so that a thermal load on the light emitting device can be reduced. Meanwhile, since the plurality of light emitting cells are electrically connected using connection electrodes or electrode layers formed on the submount substrate, it is possible to provide light emitting cell arrays connected to each other in series. Further, it is possible to provide a light emitting device capable of being directly driven by an AC power source by connecting the serially connected light emitting cell arrays in reverse parallel to each other.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/481,998, filed on Jun. 10, 2009, which is acontinuation application of U.S. patent application Ser. No. 11/721,803,filed on Jun. 14, 2007, issued as U.S. Pat. No. 7,723,736, which is aU.S. national stage application of PCT International Application No.PCT/KR2005/003555, filed on Oct. 25, 2005, and claims priority of KoreanPatent Application Nos. 10-2004-0105368, filed on Dec. 14, 2004, and10-2005-0008309, filed on Jan. 29, 2005, which are hereby incorporatedby reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device having aplurality of light emitting cells and a package having the same mountedthereon, and more particularly, to a light emitting device having aplurality of light emitting cells, which form serial arrays on a singlesubstrate and can be directly driven using an AC power source, and apackage having the same mounted thereon.

2. Discussion of the Background

A light emitting diode is an electroluminescence device having astructure in which an n-type semiconductor of which major carriers areelectrons and a p-type semiconductor of which major carriers are holesare joined together, and emits predetermined light through recombinationof these electrons and holes. Such light emitting diodes are used asdisplay devices and backlights, and their application area has expandedto the use thereof for general illumination while substituting theconventional incandescent bulbs and fluorescent lamps.

A light emitting diode consumes less electric power and has a longerservice life as compared with conventional light bulbs or fluorescentlamps. The electric power consumption of a light emitting diode is lessthan a few tenth to a few hundredth of those of conventionalillumination devices, and the life span thereof is several to severalten times, thereby having reduced electric power consumption andexcellent durability.

To use such light emitting diodes for illumination, it is necessary toeffectively dissipate heat produced from light emitting devices to theoutside. Accordingly, interest in flip-chip type light emitting devicescapable of effectively dissipating heat produced from the light emittingdevices to the outside is increasing.

FIG. 1 is a sectional view illustrating a conventional flip-chip typelight emitting device 20.

Referring to FIG. 1, first and second electrodes 12 and 14 are formed ona predetermined substrate 10, e.g., a submount substrate or a leadframe, and solders 22 and 24 are formed on these electrodes. Then, alight emitting device 20 is bonded on the substrate 10. At this time, aP-type semiconductor layer and an N-type semiconductor layer of thelight emitting device 20 are bonded to the respective solders.Thereafter, the substrate 10 with the light emitting device 20 bondedthereon is encapsulated.

Such conventional flip-chip type light emitting devices have higher heatdissipation efficiency as compared with other light emitting devicesusing bonding wires, and have improved optical efficiency because littlelight is shielded. Further, the flip-chip type light emitting deviceshave an advantage in that their packages can be compacted because theydo not use bonding wires.

However, since such a light emitting device is repeatedly turned on andoff depending on the phase of an AC power source, there is a problem inthat the light emitting device may be easily damaged. Accordingly, it isdifficult to use a light emitting device for the purpose of generalillumination by connecting it directly to a household AC power source.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light emitting devicethat can be driven by being connected directly to a AC power source.

Another object of the present invention is to provide a light emittingdevice, wherein a thermal load on the light emitting device can bereduced and light emission efficiency can be improved.

A further object of the present invention is to provide a package thatmounts the light emitting device thereon and can be driven by beingconnected directly to an AC power source.

A still further object of the present invention is to provide a lightemitting device, wherein the complication of a process of mounting thelight emitting device on a submount or a lead frame can be prevented.

To achieve these objects of the present invention, the present inventionprovides a light emitting device having a plurality of light emittingcells and a package having the same mounted thereon. A light emittingdevice according to an aspect of the present invention comprises aplurality of light emitting cells which are formed on a substrate andeach of which has an N-type semiconductor layer and a P-typesemiconductor layer located on a portion of the N-type semiconductorlayer. The plurality of light emitting cells are bonded to a submountsubstrate. Accordingly, since heat generated from the light emittingcells can be easily dissipated, a thermal load on the light emittingdevice can be reduced.

In some embodiments of the present invention, the submount substrate mayinclude a plurality of electrode layers spaced apart from one another.The plurality of light emitting cells may be bonded to the electrodelayers. At this time, the electrode layers may electrically connectN-type semiconductor layers and P-type semiconductor layers of twoadjacent light emitting cells among the plurality of light emittingcells. Accordingly, the electrode layers may serially connect theplurality of light emitting cells to a serial light emitting cell array.At least two serial light emitting cell arrays may be formed and theymay be connected in reverse parallel to each other, thereby providing alight emitting device capable of being directly driven by an AC powersource.

A conventional flip-chip light emitting device 20 means a light emittingchip with one light emitting diode formed therein. However, a lightemitting device of the present invention has a plurality of lightemitting diodes on a single substrate. Thus, the term “light emittingcell” means each of the plurality of light emitting diodes formed on thesingle substrate. Further, the term “serial light emitting cell array”means a structure in which a plurality of light emitting cells areconnected in series. Two serial light emitting cell arrays on the singlesubstrate can be connected to be driven by respective currents flowingin opposite directions. Accordingly, the light emitting device can beconnected directly to an AC power source without the use of an AC-to-DCconverter or the like, so that the light emitting device can be used forgeneral illumination.

In the meantime, the light emitting device may further include an N-typemetal bumper formed on each of the N-type semiconductor layers and aP-type metal bumper formed on each of the P-type semiconductor layers.The plurality of light emitting cells are bonded to the electrode layersthrough the N-type and P-type metal bumpers. Accordingly, the pluralityof light emitting cells are electrically connected to the electrodelayers through the metal bumpers, and at the same time, heat can beeasily dissipated to the submount substrate through the metal bumpers.

The submount substrate may have a plurality of concave portions andconvex portions, and the N-type semiconductor layers and the P-typesemiconductor layers may be bonded to the convex portions and theconcave portions, respectively. The concave portions and the convexportions can be defined as N-regions and P-regions, respectively. Atthis time, each of the electrode layers is formed over the P-region andthe N-region to connect the P-region and the N-region.

In the embodiments of the present invention, the submount substrate mayinclude a P-type bonding pad formed at an edge thereof and an N-typebonding pad formed at the other edge thereof.

In the meantime, among the plurality of light emitting cells, a P-typesemiconductor layer of a light emitting cell located at the edge of thesubstrate may be electrically connected to the P-type bonding pad, andan N-type semiconductor layer of a light emitting cell located at theother edge of the substrate may be electrically connected to the N-typebonding pad.

The P-type semiconductor layer and the P-type bonding pad may beelectrically connected to each other through a P-type metal bumper, andthe N-type semiconductor layer and the N-type bonding pad may beelectrically connected to each other through an N-type metal bumper.

In some embodiments of the present invention, instead of the electrodelayers of the submount substrate, a plurality of connection electrodesmay connect the N-type semiconductor layers and the P-type semiconductorlayers of adjacent light emitting cells between the light emitting celllocated at the edge of the substrate and the light emitting cell locatedat the other edge of the substrate, thereby forming a serial lightemitting cell array on the substrate. According to this embodiments,since there is no need for aligning the N-type semiconductor layers andthe P-type semiconductor layers of the light emitting cells with theelectrode layers, the process of mounting the plurality of lightemitting cells on the submount substrate can be simplified.

Meanwhile, each of the plural light emitting cells may include a bufferlayer formed on the substrate. The N-type semiconductor layer may beformed on the buffer layer, and an active layer may be located on aportion of the N-type semiconductor layer. Further, the P-typesemiconductor layer may be located on the active layer. In addition, afirst metal layer may be formed on the P-type semiconductor layer, and asecond metal layer may be formed on the first metal layer. The firstmetal layer may be a transparent electrode, and the second metal layermay he a reflective film.

A light emitting device according to another aspect of the presentinvention comprises a plurality of light emitting cells formed on asubstrate. Each of the plural light emitting cells has an N-typesemiconductor layer and a P-type semiconductor layer located on aportion of the N-type semiconductor layer. Meanwhile, an N-type metalbumper is formed on an N-type semiconductor layer of one light emittingcell among the plurality of light emitting cells, and a P-type metalbumper is formed on a P-type semiconductor layer of another lightemitting cell among the plurality of light emitting cells. The lightemitting device is mounted on a lead frame or a submount substratethrough the N-type metal bumper and the P-type metal bumper.

In some embodiments of the present invention, in addition to the N-typemetal bumper, other N-type metal bumpers may be formed on N-typesemiconductor layers of light emitting cells except the above one lightemitting cell among the plurality of light emitting cells, and inaddition to the P-type metal bumper, other P-type metal bumpers may beformed on P-type semiconductor layers of light emitting cells except theabove another light emitting cell among the plurality of light emittingcells. A serial light emitting cell array may be formed by formingelectrode layers on the submount substrate and electrically connectingthe N-type and P-type metal bumpers through the electrode layers.

On the contrary, a serial light emitting cell array may be formed on thesubstrate by electrically connecting the N-type semiconductor layers andthe P-type semiconductor layers of the adjacent light emitting cellswith a plurality of connection electrodes. At this time, the above onelight emitting cell and the above another light emitting cell may belocated at both ends of the serial light emitting cell array. Inaddition, a top surface of the N-type metal bumper formed on the N-typesemiconductor layer of the one light emitting cell and a top surface ofthe P-type metal bumper formed on the P-type semiconductor layer of theother light emitting cell may be at least flush with top surfaces of theconnection electrodes. That is, the top surfaces of the connectionelectrodes may be located below or at the same level as the top surfacesof the N-type and P-type metal bumpers. If the top surfaces of theconnection electrodes are located below the top surfaces of the metalbumpers, a short circuit between the connection electrodes and thesubmount substrate or lead frame can be prevented. If the top surfacesof the connection electrodes are located at the same level as the topsurfaces of the bonding pads, the top surfaces of the connectionelectrodes may be in direct contact with the submount substrate or leadframe, thereby promoting dissipation of heat.

A further aspect of the present invention provides a submount substratefor mounting a plurality of light emitting cells thereon. The submountsubstrate includes a substrate having a plurality of N-regions andP-regions defined thereon. A plurality of electrode layers are locatedon the substrate while being spaced apart from one another. Theelectrode layers connect adjacent N-regions and P-regions. At this time,a dielectric film may be located beneath the plurality of electrodeslayers.

In the meantime, the substrate may have concave portions and convexportions, and the convex portions and the concave portions may bedefined as the N-regions and the P-regions, respectively.

A still further aspect of the present invention provides a package onwhich a light emitting device having a plurality of light emitting cellsis mounted. The package comprises a lead frame having metal leads. Alight emitting device is located on the lead frame. The light emittingdevice includes a plurality of light emitting cells formed on asubstrate. Each of the plurality of light emitting cells has an N-typesemiconductor layer, and a P-type semiconductor layer located on aportion of the N-type semiconductor layer. A plurality of connectionelectrodes may electrically connect N-type semiconductor layers andP-type semiconductor layers of adjacent light emitting cells, therebyforming a serial light emitting cell array on the substrate. Inaddition, metal bumpers may be located at both ends of the serial lightemitting cell array. The metal bumpers may be electrically connected tothe metal leads. Accordingly, even though there are the plurality oflight emitting cells, bonding can be simplified since the metal bumperslocated at the both ends of the serial light emitting cell array areconnected to the metal leads. The complication of the process ofmounting the light emitting device can be prevented, as compared with aconventional process of mounting a flip-chip type light emitting device.

In addition, a submount substrate may be interposed between the leadframe and the light emitting device. The submount substrate may havebonding pads corresponding to the metal bumpers on a top surfacethereof. The bonding pads may be electrically connected to the metalleads.

The bonding pads may be electrically connected to the metal leadsthrough bonding wires or directly to the metal leads through a circuitformed on the submount substrate.

Meanwhile, the connection electrodes of the light emitting device maycome into contact with the top surface of the submount substrate. Atthis time, heat generated from the light emitting device can bedissipated through the submount substrate, thereby promoting thedissipation of heat. On the contrary, the connection electrodes may bespaced apart from the top surface of the submount substrate.Accordingly, a short circuit between the connection electrodes and themetal leads can be easily prevented.

According to the present invention, there is provided a light emittingdiode that can be driven through direct connection to an AC power sourceby employing serial light emitting cell arrays having a plurality oflight emitting cells connected in series. Since a flip-chip type lightemitting device having a plurality of light emitting cells connected inseries is implemented, heat generated from the light emitting cells canbe easily dissipated, thereby reducing a thermal load on the lightemitting device and improving light emitting efficiency as well.Meanwhile, it is possible to provide a package that can be driventhrough direct connection to an AC power source by mounting the lightemitting device thereon. Moreover, even though the plurality of lightemitting cells are employed, the process of mounting the plurality oflight emitting cells on a submount substrate or lead frame can besimplified since the plurality of light emitting cells are connected inseries using connection electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating a conventional flip-chip typelight emitting device.

FIG. 2 is a circuit diagram illustrating an operational principle of alight emitting device having a plurality of light emitting cellsaccording to an embodiment of the present invention.

FIGS. 3 and 4 are sectional views illustrating a light emitting cellblock of a flip-chip type light emitting device according to anembodiment of the present invention.

FIG. 5 is a sectional view illustrating a flip-chip type submountsubstrate according to an embodiment of the present invention.

FIG. 6 is a sectional view illustrating a light emitting device havingthe light emitting cell block of FIG. 4 mounted on the submountsubstrate of FIG. 5 according to an embodiment of the present invention.

FIG. 7 is a sectional view illustrating a light emitting device having aplurality of light emitting cells mounted on a submount substrateaccording to another embodiment of the present invention.

FIG. 8 is a sectional view illustrating a light emitting device having alight emitting cell block mounted on a submount substrate according to afurther embodiment of the present invention.

FIGS. 9 and 10 are sectional views illustrating light emitting devicesaccording to still further embodiments of the present invention.

FIGS. 11 to 13 are sectional views illustrating packages having thelight emitting device of FIG. 10 mounted thereon.

FIG. 14 and FIG. 15 are sectional views illustrating a light emittingdevice having a plurality of light emitting cells mounted on a submountsubstrate according to exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The followingembodiments are provided only for illustrative purposes so that thoseskilled in the art can fully understand the spirit of the presentinvention. Therefore, the present invention is not limited to thefollowing embodiments but may be implemented in other forms. In thedrawings, the widths, lengths, thicknesses and the like of elements canbe exaggerated for convenience of illustration. Like reference numeralsindicate like elements throughout the specification and drawings.

FIG. 2 is a circuit diagram illustrating an operational principle of alight emitting device having a plurality of light emitting cellsaccording to an embodiment of the present invention.

Referring to FIG. 2, a first serial array 31 is formed by connectinglight emitting cells 31 a, 31 b and 31 c in series, and a second serialarray 33 is formed by connecting other light emitting cells 33 a, 33 band 33 c in series.

Both ends of each of the first and second serial arrays 31 and 33 areconnected to an AC power source 35 and a ground, respectively. The firstand second serial arrays are connected in parallel between the AC powersource 35 and the ground. That is, both ends of the first serial arrayare electrically connected to those of the second serial array.

Meanwhile, the first and second serial arrays 31 and 33 are arrangedsuch that their light emitting cells are driven by currents flowing inopposite directions. In other words, as shown in the figure, anodes andcathodes of the light emitting cells included in the first serial array31 and anodes and cathodes of the light emitting cells included in thesecond array 33 are arranged in opposite directions.

Thus, if the AC power source 35 is in a positive phase, the lightemitting cells included in the first serial array 31 are turned on toemit light, and the light emitting cells included in the second serialarray 33 are turned off. On the contrary, if the AC power source 35 isin a negative phase, the light emitting cells included in the firstserial array 31 are turned off, and the light emitting cells included inthe second serial array 33 are turned on.

Consequently, the first and second serial arrays 31 and 33 arealternately turned on and off by the AC power source so that the lightemitting device including the first and second serial arrays continuesto emit light.

Although light emitting chips, each of which comprises a single lightemitting diode, can be connected to one another to be driven by an ACpower source as in the circuit of FIG. 2, the space occupied by thelight emitting chips may be increased. However, in the light emittingdevice of the present invention, a single chip can be driven by beingconnected to an AC power source, thereby preventing an increase in spaceoccupied by the light emitting device.

Meanwhile, although the circuit shown in FIG. 2 is configured such thatthe both ends of each of the first and second serial arrays areconnected to the AC power source 35 and the ground, respectively, thecircuit may be configured such that the both ends thereof are connectedto both terminals of the AC power source, Further, although each of thefirst and second serial arrays comprises three light emitting cells,this is only an illustrative example for better understanding and thenumber of light emitting cells may be increased, if necessary. Thenumber of serial arrays may also be increased.

In the meantime, a bridge rectifier may be arranged between an AC powersource and a serial array to provide a light emitting device driven bythe AC power source. At this time, the bridge rectifier may beconfigured using the light emitting cells. By adopting such a bridgerectifier, it is possible to provide a light emitting device with onlyone serial array, which can be driven by the AC power source.

FIGS. 3 and 4 are sectional views illustrating a light emitting cellblock 1000 of a flip-chip type light emitting device according to anembodiment of the present invention, and FIG. 5 is a sectional viewillustrating a flip-chip type submount substrate 2000 according to anembodiment of the present invention.

Referring to FIGS. 3 and 4, the light emitting cell block 1000 has aplurality of light emitting cells arrayed on a sapphire substrate 110.Each of the light emitting cells includes a buffer layer 120 formed onthe substrate 110, an N-type semiconductor layer 130 formed on thebuffer layer 120, an active layer 140 formed on a portion of the N-typesemiconductor layer 130, and a P-type semiconductor layer 150 formed onthe active layer 140. Further, a first metal layer 160 is formed on theP-type semiconductor layer 150. Meanwhile, a P-type metal bumper 170 isformed on the first metal layer 160 and an N-type metal bumper 180 isformed on the N-type semiconductor layer 130. Also, a second metal layer(not shown) having a reflectivity of 10 to 100% may be formed on thefirst metal layer 160 and the N-type semiconductor layer 130. Moreover,an additional ohmic metal layer for smooth supply of a current may befomied on the P-type semiconductor layer 150.

The substrate 110 may be a substrate made of Al₂O₃, SiC, ZnO, Si, GaAs,GaP, LiAl₂O₃, BN, AlN or GaN. The substrate 110 is selected inconsideration of a lattice coefficient of a semiconductor layer formedthereon. For example, in a case where a GaN based semiconductor layer isformed on the substrate 110, a sapphire substrate 110 or a SiC substratecan be selected as the substrate 110. In this embodiment, the bufferlayer 120 performing a buffering function is formed when the N-typesemiconductor layer 130 is formed on the substrate 110. However, it isnot limited thereto, and the buffer layer 120 may not be formed.

Although a gallium nitride (GaN) film doped with N-type impurities canbe used as the N-type semiconductor layer 130, it is not limitedthereto, and various semiconductor material layers may be used. In thisembodiment, the N-type semiconductor layer 130 is formed to include anN-type AlGa_(1-x)N (0≦x≦1) film. Further, a gallium nitride film dopedwith P-type impurities can used as the P-type semiconductor layer 150.In this embodiment, the P-type semiconductor layer 150 is formed toinclude a P-type AlGa_(1-x)N (0≦x≦1) film. Meanwhile, an InGaN film maybe used as the semiconductor layer. Moreover, each of the N-typesemiconductor layer 130 and the P-type semiconductor layer 150 may beformed as a multi-layered film, Si is used as the N-type impurities, andZn and Mg are used as the P-type impurities for InGaAlP and a nitridebased compound, respectively.

Further, a multi-layered film having quantum well layers and barrierlayers repeatedly formed on an N-type AlGa_(1-x)N (0≦x≦1) film is usedas the active layer 140. The barrier well layer and quantum well layermay be made of a binary compound such as GaN, InN or AlN, a tertiarycompound such as In_(x)Ga_(1-x)N (0≦x≦1) or Al_(x)Ga_(1-x)N (0≦x≦1), ora quaternary compound such as Al_(x)In_(x)Ga_(1-x-y)N (0≦x+y≦1). Thebinary to quaternary compounds maybe doped with N-type or P-typeimpurities.

It is preferred that a transparent electrode film he used as the firstmetal layer 160. In this embodiment, ITO is used. A reflective film withelectric conductivity is used as the second metal layer. The N-type andP-type metal bumpers 170 and 180 may be made of at least one of Pb, Sn,Au, Ge, Cu, Bi, Cd, Zn, Ag, Ni and Ti.

A method of fabricating the light emitting cell block 1000 with theaforementioned structure will be briefly described below.

The buffer layer 120, the N-type semiconductor layer 130, the activelayer 140 and the P-type semiconductor layer 150 are sequentially formedon the substrate 110.

These material layers are formed through various deposition and growthmethods including metal organic chemical vapor deposition (MOCVD),molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), andthe like.

The P-type semiconductor 150, the active layer 140, the N-typesemiconductor layer 130 and the buffer layer 120 are partially removedto separate the light emitting cells. To this end, a predetermined maskpattern (not shown) is formed on the P-type semiconductor layer 150, andportions of the P-type semiconductor 150, the active layer 140, theN-type semiconductor layer 130 and the buffer layer 120, which areexposed through the mask pattern, are etched so that the plurality oflight emitting cells are electrically separated from one another.

Then, the P-type semiconductor 150 and the active layer 140 arepartially removed through a predetermined etching process to expose aportion of the N-type semiconductor layer 130. For example, an etchingmask pattern for exposing a portion of the P-type semiconductor layer150 is formed thereon, and exposed portions of the P-type semiconductorlayer 150 and the active layer 140 are then removed through a dry or wetetching process so that the N-type semiconductor layer 130 can bepartially exposed. At this time, an upper portion of the N-typesemiconductor layer 130 maybe partially removed simultaneously.

Thereafter, the first metal layer 160 is formed on the P-typesemiconductor layer 150. The first metal layer 160 can be formed using alift-off process. That is, a photoresist is applied on the entirestructure, and a first photoresist pattern (not shown) for exposing theP-type semiconductor layer 150 is then formed through a lithographic anddeveloping process using a predetermined mask. Subsequently, the firstmetal layer 160 is formed on the entire structure, and the firstphotoresist pattern is then removed. As a result, a portion of the metallayer 160 except another portion thereof located on the P-typesemiconductor layer 150 is removed so that the first metal layer 160remains on the P-type semiconductor layer 150.

The P-type metal bumper 170 is formed on the first metal layer 160, andthe N-type metal bumper 180 is formed on the N-type semiconductor layer130. To this end, a photoresist is applied on the entire structure, anda second photoresist pattern (not shown) for exposing a portion of thefirst metal layer 160 and a portion of the N-type semiconductor layer130 is then formed through the lithographic and developing process usinga predetermined mask. Then, a metal layer is deposited on the entirestructure, and portions of the metal layer except a portion thereofformed on the exposed portion of the first metal layer 160 and a portionthereof formed on the exposed portion of the N-type semiconductor layer130 and the second photoresist pattern are then removed.

As a result, the P-type metal bumper 170 is formed on the first metallayer 160, and the N-type metal bumper 180 is formed on the N-typesemiconductor layer 130.

The process of fabricating the light emitting cell block for a flip-chiptype light emitting device according to the present invention is notlimited to the aforementioned method but various modifications andmaterial films may be further added thereto. That is, after the firstmetal layer is formed on the P-type semiconductor layer, the etchingprocess of separating the light emitting cells may be performed.Further, after the N-type semiconductor layer is exposed, the exposedportion of the N-type semiconductor layer and a portion of the bufferlayer below the portion of the N-type semiconductor layer may be removedto separate the light emitting cells. Moreover, a second metal layerformed of a metallic reflective film may be further formed on the firstmetal layer.

FIG. 5 is a sectional view illustrating a submount substrate 2000 for aflip-chip type light emitting device according to an embodiment of thepresent invention.

Referring to FIG. 5, the submount substrate 2000 comprises a substrate200 having a plurality of N-regions B and P-regions A defined thereon, adielectric film 210 formed on the substrate 200, and a plurality ofelectrode layers 230 each of which unitarily connects adjacent N-regionB and P-region A to each other. The submount substrate further comprisesa P-type bonding pad 240 extending to the P-region A located at an edgeof the substrate, and an N-type bonding pad 250 extending to theN-region B located at the other edge thereof.

The N-regions B refer to regions to which the N-type metal bumpers 180in the light emitting cell block 1000 are connected, and the P-regions Arefer to regions to which the P-type metal bumpers 170 in the lightemitting cell block 1000 are connected.

At this time, various materials with thermal conductivity can be usedfor the substrate 200 and, for example, SiC, Si, Ge, SiGe, AlN, metaland the like can be used. In a case where the substrate 200 isconductive, the dielectric film 210 electrically insulates theelectrodes 230 and the bonding pads 240 and 250 from the substrate 200.The dielectric film 210 can be formed as a multi-layered film. Thedielectric film 210 may be made of, for example, at least one of SiO₂,MgO and SiN.

The electrode layer 230, the N-type bonding pad 250 and the P-typebonding pad 240 are made of a metal with superior electricalconductivity.

A method of fabricating the submount substrate 2000 will be describedbelow.

Concave portions and convex portions are formed on the substrate 200 todefine the N-regions B and the P-regions A thereon. The widths, heightsand shapes of the N-regions B and P-regions A may be modified variouslydepending on the sizes of the N-type metal bumpers 180 and the P-typemetal bumpers 170. In this embodiment, the convex portions of thesubstrate 200 become the N-regions B, and the concave portions of thesubstrate 200 become the P-regions A. The substrate 200 with such ashape may be fabricated using a molding technique or through an etchingprocess. That is, a mask for exposing the P-regions A is formed on thesubstrate 200, and exposed portions of the substrate 200 are then etchedto form the recessed P-regions A. Then, the mask is removed so that therecessed P-regions A and the relatively protruding N-regions B areformed. Alternatively, the recessed P-regions A may be formed by meansof machining.

Then, the dielectric film 210 is formed on the entire structure, i.e.,the substrate 200 with the concave portions and the convex portions. Atthis time, the dielectric film 210 may not be formed in a case where thesubstrate 200 is not made of a conductive material. In this embodiment,a metallic material with superior electrical conductivity is used as thesubstrate 200 to improve thermal conductivity. Thus, the dielectric film210 is formed to function as a sufficient insulator.

Next, the electrode layers 230 each of which connects adjacent N-regionB and P-region A in pair are formed on the dielectric film 210. Theelectrode layers 230 may be formed through a screen printing method, ora vapor deposition process using a predetermined mask pattern.

Thereafter, the aforementioned light emitting cell block 1000 is bondedto the submount substrate 2000 so that a light emitting device isfabricated.

FIG. 6 is a sectional view illustrating a light emitting device havingthe light 20 emitting cell block 1000 mounted on the submount substrate2000.

Referring to FIG. 6, the P-type and N-type metal bumpers 170 and 180 ofthe light emitting cell block 1000 arc bonded to the N-regions B andP-regions A of the submount substrate 2000, and the N-type metal bumper180 and the P-type metal bumper 170 of two adjacent light emitting cellsarc connected to each other by the electrode layer 230 of the submountsubstrate 200, as shown in the figure. The P-type metal bumper 170located at one edge of the light emitting cell block 1000 is connectedto the P-type bonding pad 240 of the submount substrate 2000, and theN-type metal bumper 180 located at the other edge of the light emittingcell block 1000 is connected to the N-type bonding pad 250 of thesubmount substrate 2000.

At this time, the metal bumpers 170 and 180, the electrode layers 230,and the bonding pads 240 and 250 can be bonded through various bondingmethods, e.g., an eutectic method using the eutectic temperature. As aresult, the plurality of light emitting cells are bonded to the top ofthe submount substrate 2000, so that light emitting cell arraysconnected in series are formed.

At this time, the number of the light emitting cells connected in seriescan be variously modified depending on an electric power source to beused and power consumption of the light emitting cells.

Preferably, a light emitting cell block 1000 with 10 to 1,000 lightemitting cells formed thereon is bonded to the submount substrate 2000to fabricate a light emitting device with the light emitting cellsserially connected by the substrate 2000. More preferably, a lightemitting cell block 1000 with 15 to 50 light emitting cells formedthereon is bonded to the submount substrate 2000 to fabricate a lightemitting device with the light emitting cells serially connected by thesubstrate 2000. For example, when driven by a 220V AC power source, itis possible to fabricate a flip-chip type light emitting device with 66or 67 unit light emitting cells of 3.3V at a certain driving current,which are bonded to the submount substrate 2000. Further, when driven bya 110V AC power source, it is possible to fabricate a light emittingdevice with 33 or 34 unit light emitting cells of 3.3V at a certaindriving current, which are serially bonded to the submount substrate2000.

The bonding method of the present invention is not limited thereto, andvarious embodiments can be made.

For example, instead of the light emitting cell block 1000 with theplurality of light emitting cells connected by the substrate 110 shownin FIG. 6, individual light emitting cells 100 a, 100 b and 100 c may belocated on the submount substrate 2000 while being spaced apart from oneanother as shown in FIG. 7. At this time, the N-type metal bumpers 170and the P-type metal bumpers 180 of adjacent light emitting cells 100 ato 100 c are electrically connected to each other by the electrodelayers 230 formed on the submount substrate 2000.

The light emitting cells 100 a, 100 b and 100 c of FIG. 7 are fabricatedby separating the substrate 110 from the plurality of light emittingcells in the light emitting cell block 1000 of FIG. 6. Alternatively,the light emitting cells 100 a, 100 b, and 100 c can be fabricated bypartially separating the substrate 110 from each of the light emittingcells, as shown in FIG. 15. The substrate 110 can be separated from thelight emitting cells using a laser or a grinding process.

In another exemplary embodiment of the present invention, as FIG. 14shows, the light emitting cells 100 a, 100 b and 100 c may be fabricatedby separating the substrate 110 from the plurality of light emittingcells in the light emitting cell block 1000 of FIG. 6. In this case,however, the light emitting cell block 1000 is formed without the bufferlayer 120.

Alternatively, as shown in FIG. 8, a light emitting device can befabricated by forming electrode layers 230, which connect adjacentN-regions B and P-regions A in pairs, on a flat substrate 200 with theplurality of N-regions B and P-regions A defined thereon so as to form asubmount substrate 2000, and by mounting a light emitting cell block onthe submount substrate 2000. That is, the electrode layers 230 spacedapart from one another are formed on the substrate 200 on which certainpatterns, e.g., concave portions and convex portions, are not formed,and the N-type metal bumpers 180 and the P-type metal bumpers 170 ofadjacent light emitting cells are electrically connected to each other.At this time, the N-type metal bumpers 180 and the P-type metal bumpers170 are bonded to the electrode layers 230 at the same level, as shownin the figure.

Meanwhile, instead of formation of the P-type and N-type metal bumpers170 and 180 on the light emitting cells, the metal bumpers 170 and 180may be formed on the N-regions B and P-regions A on the submountsubstrate 2000. At this time, certain metal electrodes (not shown) maybe further formed on the N-type and P-type semiconductor layers 130 and150 so as to be bonded to the metal bumpers 170 and 180.

In the embodiments of the present invention, the light emitting cellsformed on the substrate 110 can be connected by the electrode layers 230to form at least two serial light emitting cell arrays. The at least twoserial light emitting cell arrays can be driven by a household AC powersource while being connected in reverse parallel to each other. On thecontrary, an additional bridge circuit may be configured within thelight emitting device. The bridge circuit may be configured using thelight emitting cells and the electrode layers.

In the aforementioned embodiments, the electrode layers of the submountsubstrate 2000 electrically connect the plurality of light emittingcells to one another to form the serial light emitting cell arrays.However, since the plurality of light emitting cells should be alignedwith the electrode layers of the submount substrate 2000, it may becomplicated to bond the plurality of light emitting cells to thesubmount substrate 2000 in the present embodiments.

A light emitting device capable of preventing the process of bonding aplurality of light emitting cells to a submount substrate or a leadframe from being complicated according to another embodiment of thepresent invention will be described below.

FIG. 9 is a sectional view illustrating a light emitting device 50according to a still further embodiment of the present invention.

Referring to FIG. 9, the light emitting device 50 comprises a substrate51 and a plurality of light emitting cells formed on the substrate. Thesubstrate 51 is selected in consideration of a lattice coefficient of asemiconductor layer to be formed thereon.

For example, in a case where a GaN based semiconductor layer is formedon the substrate 51, the substrate 51 may be a sapphire substrate.

Each of the light emitting cells comprises an N-type semiconductor layer55, an active layer 57 and a P-type semiconductor layer 59. The activelayer 57 is located on a portion of the N-type semiconductor 55, and theP-type semiconductor layer 59 is located on the active layer 57.Accordingly, a portion of a top surface of the N-type semiconductorlayer is covered with the active layer 57 and the P-type semiconductorlayer 59, and the remainder of the top surface of the N-typesemiconductor layer is exposed. Meanwhile, a metal layer 61 may belocated on the P-type semiconductor layer 59, and another metal layer 63may be located on the other portion of the N-type semiconductor layer55. The metal layers 61 and 63 form ohmic contacts with the P-type andN-type semiconductor layers to lower junction resistance, At this time,although the other metal layer 63 may be made of a material identicalwith a metallic material included in the metal layer, it is not limitedthereto. Further, if there is no need for a metal layer for forming anadditional ohmic contact, the metal layer 63 will be eliminated.

In the meantime, a buffer layer 53 may be interposed between the N-typesemiconductor layer 55 and the substrate 51. The buffer layer 53 is usedto reduce stress due to difference between lattice coefficients of thesubstrate 51 and the Ntype semiconductor layer 55. As the buffer layer,a GaN based semiconductor layer can be used.

Although the N-type semiconductor layer 55 can be a GaN based film dopedwith N-type impurities, e.g., an N-type Al_(x)Ga_(1-x)N (0≦x≦1), it isnot limited thereto, and may be formed of various semiconductor layers.Further, although the P-type semiconductor layer 59 can be a GaN basedfilm doped with P-type impurities, e.g., a P-type Al_(x)Ga_(1-x)N(0≦x≦1) film, it is not limited thereto, and may be formed of varioussemiconductor layers. The N-type and P-type semiconductor layers may beIn_(x)Ga_(1-x)N (0≦x≦1) films and formed into multi-layered films.Meanwhile, Si maybe used as the N-type impurities, and Mg may be used asthe P-type impurities. If the semiconductor layer is based on GaP ratherthan GaN, Zn may be used as the P-type impurities.

The active layer 57 generally has a multi-layered film structure inwhich quantum well layers and barrier layers are repeatedly formed. Thequantum well layers and the barrier layers may be formed using anAl_(x)In_(x)Ga_(1-x-y)N (0≦x, y≦1, 0≦x+y≦1) compound and may be dopewith N-type or P-type impurities.

In addition, the metal layer 61 may include first and second metallayers laminated one above another. The first metal layer and the secondmetal layer may be a transparent electrode layer and a reflective layer,respectively. The reflective layer improves optical efficiency byreflecting light, which has been emitted from the active layer and thentransmitted through the transparent electrode layer, back to thesubstrate 51. The transparent electrode layer may be an indium-tin oxide(ITO) film, and the reflective layer may be a metal layer withreflectivity of 10 to 100%.

The light emitting cells can be fabricated by sequentially forming abuffer layer, an N-type semiconductor layer, an active layer and aP-type semiconductor layer on the substrate 51, and by etching themusing a lithographic and etching process. At this time, the materiallayers can be formed through various deposition and growth methods suchas metal organic chemical vapor deposition (MOCVD), molecular beamepitaxy (MBE), and hydride vapor phase epitaxy (HVPE). Before thelithographic and etching process is performed, a metal layer may befurther formed on the P-type semiconductor layer.

After the light emitting cells are separated from one another using thelithographic and etching process, other metal layers 63 may be formed.The other metal layers may be formed by depositing metal layers on theseparated light emitting cells and patterning the metal layers using thelithographic and etching process.

In the meantime, the N-type semiconductor layers and the P-typesemiconductor layers of adjacent light emitting cells are electricallyconnected by respective connection electrodes 65. The light emittingcells are serially connected by the connection electrodes 65 to form aserial light emitting cell array. As described with reference to FIG. 2,at least two serial light emitting cell arrays may be formed on thesubstrate 51. The at least two serial light emitting cell arrays arearranged to be driven with currents flowing in opposite directions.

In the case where the metal layers 61 and 63 are formed on the N-typeand P-type semiconductor layers 55 and 59, the connection electrodes 65connect the metal layers 61 on the P-type semiconductor layers and themetal layers 63 on the N-type semiconductor layers. The connectionelectrodes 65 can connect the metal layers in the form of an air bridgeor step-cover. The connection electrodes 65 can be formed using metalvapor deposition, electroplating or electroless plating.

In the meantime, metal bumpers 67 a and 67 b are located on both ends ofthe serial light emitting cell array. The metal bumpers 67 a and 67 bare metal bumpers performing a bumping function when the light emittingdevice 50 is mounted later on a submount substrate or a lead frame.

The thickness of the metal bumper 67 a may be 0.01 to 100 μm, and topsurfaces of the metal bumpers 67 a and 67 b are located at a levelhigher than that of the connection electrodes 65.

Meanwhile, metal bumpers may be formed at all both ends of the seriallight emitting cell arrays but are not limited thereto. Metal bumpersmay be formed at both ends of one serial array, and both ends of each ofother serial arrays may be electrically connected to the metal bumpers.

The light emitting device 50 according to the embodiment of the presentinvention can be operated by being connected directly to an AC powersource. Since the light emitting cells are connected to one another bythe connection electrodes 65, the light emitting device 50 can beoperated by bonding the metal bumpers 67 a and 67 b to a submountsubstrate or a lead frame. Therefore, even though there are theplurality of light emitting cells, it is possible to prevent the processof mounting the light emitting device 50 from being complicated.

FIG. 10 is a sectional view illustrating a light emitting device 70according to a still further embodiment of the present invention.

Referring to FIG. 10, the light emitting device 70 comprises the samecomponents as the light emitting device 50 described with reference toFIG. 9. Only parts of the light emitting device 70 different from thoseof the light emitting device 50 will be described below.

The light emitting device 70 of this embodiment has connectionelectrodes 75 located at the same level as the top surfaces of the metalbumpers 67 a and 67 b. Therefore, the metal bumpers 67 a and 67 b can beformed using a process identical with the process of forming theconnection electrodes 75. Further, since the connection electrodes arcalso in contact with the top of a submount substrate or lead frame, thelight emitting device 70 can improve heat dissipation as compared withthe light emitting device 50 of FIG. 9.

FIGS. 11 to 13 are sectional views illustrating packages having thelight emitting device 70 according to other embodiments of the presentinvention. FIG. 11 is a sectional view illustrating a package with thelight emitting device 70 mounted on a lead frame, and FIGS. 12 and 13are sectional views illustrating packages with the light emitting device70 mounted on a submount substrate.

Referring to FIG. 11, a package 3000 comprises a lead frame with metalleads 101 a and 101 b. The lead frame can include a package body 103 inwhich the metal leads are insert-molded. Further, the lead frame may bea printed circuit board.

The light emitting device 70 is mounted on the lead frame and thenelectrically connected to the metal leads 101 a and 101 b. At this time,the metal bumpers 67 a and 67 b of the light emitting device 70 arebonded to the metal leads 101 a and 101 b, respectively. As a result,the serial light emitting cell arrays of the light emitting device 70are electrically connected to the metal leads 101 a and 101 b.Meanwhile, the connection electrodes 75 are in physical contact with atop surface of the lead frame while being spaced apart from the metalleads. Therefore, heat generated from the light emitting device 70 canbe easily dissipated to the lead frame through the connection electrodes75.

A molding member 105 covers the top of the light emitting device 70. Themolding member may contain a fluorescent substance and/or a diffusingsubstance. The fluorescent substance can convert a portion of lightemitted from the light emitting device 70 into light with a longerwavelength. Thus, white light can be obtained using a light emittingdevice 70 emitting ultraviolet rays or blue light. Meanwhile, thefluorescent substance can be interposed between the molding member 105and the light emitting device 70. The molding member 105 can have a lensshape to adjust a directional angle of emitted light.

In the meantime, the package 3000 can further include a heat sink 107beneath the package body 103. The heat sink 107 promotes dissipation ofheat emitted from the light emitting device 70.

According to this embodiment, there is provided a package 3000 that canbe driven through direct connection to an AC power source by mountingthe light emitting device 70 with the plurality of light emitting cells.Further, since the connection electrodes 75 are in physical contact withthe top surface of the lead frame, the dissipation of the heat generatedfrom the light emitting device 70 can be promoted.

Meanwhile, instead of the light emitting device 70, the light emittingdevice 50 of FIG. 9 may be mounted. At this time, since the connectionelectrodes 65 of the light emitting device 50 have a lower height ascompared with the metal bumpers 67 a and 67 b, they do not come intophysical contact with the top surface of the lead frame. Therefore, ashort circuit between the connection electrodes 65 and the metal leads101 a and 101 b can be easily prevented.

Referring to FIG. 12, a package 4000 according to this embodiment isconfigured by adding a submount substrate 201 and bonding wires 203 aand 203 b to the package 3000 described with reference to FIG. 11. Thesubmount substrate 201 is interposed between the light emitting device70 and a top surface of a lead frame.

The submount substrate 201 includes a substrate and bonding pads 201 aand 201 b formed on the substrate. The bonding pads correspond to themetal bumpers 67 a and 67 b of the light emitting device 70. The metalbumpers of the light emitting device are bonded to the bonding pads ofthe submount substrate.

It is preferred that the substrate of the submount substrate be made ofa material with thermal conductivity. A substrate made of SiC, Si,germanium (Ge), silicone germanium (SiGe), aluminum nitride (AIN), metalor the like can he used as the substrate. Meanwhile, a dielectric layermay be formed on a top surface of the substrate. The dielectric layerinsulates the bonding pads 201 a and 201 b and the connection electrodes75 from the substrate. Meanwhile, if the substrate is made of aninsulating material, the dielectric layer can be eliminated.

The bonding pads 201 a and 201 b, and the metal leads 101 a and 101 bare electrically connected through bonding wires.

As described with reference to FIG. 11, instead of the light emittingdevice 70, 15 the light emitting device 50 of FIG. 9 may be mounted.

Referring to FIG. 13, a package 5000 according to this embodiment has asubmount substrate 301 interposed between the light emitting device 70and the lead frame, in the same manner as the package illustrated inFIG. 12. However, the submount substrate 301 is different from thesubmount substrate 201 of FIG. 12 in that it has bonding pads 301 a and301 b penetrating through the submount substrate. Accordingly, since thebonding pads are bonded directly to the metal leads 101 a and 101 b, thebonding wires of FIG. 12 can be eliminated.

The submount substrate 301 is not limited thereto but may be variouslymodified. For example, the bonding pads 301 a and 301 b may notpenetrate through the submount substrate but extend to the bottom of thesubmount substrate along the sides of the substrate, respectively.

Further, instead of the light emitting device 70, the light emittingdevice 50 of FIG. 9 may be mounted on the submount substrate 301.

1. A light emitting diode package, comprising: a substrate; a nitridesemiconductor light emitting cell arranged on the substrate, a topsurface of the nitride semiconductor light emitting cell comprising ann-type nitride semiconductor layer or an un-doped nitride semiconductorlayer, a bottom surface of the nitride semiconductor light emitting cellcomprising a p-type nitride semiconductor layer and a partially exposedn-type nitride semiconductor layer; a passivation layer arranged betweenthe substrate and the nitride semiconductor light emitting cell; a firstmetal layer arranged between the substrate and the nitride semiconductorlight emitting cell, the first metal layer contacting the bottom surfaceof the nitride semiconductor light emitting cell; a molding memberarranged on the nitride semiconductor light emitting cell; and a firstbonding pad connected to the first metal layer, the first bonding padpenetrating through the substrate.
 2. The light emitting device of claim1, further comprising a transparent layer covering the top surface ofthe nitride semiconductor light emitting cell, wherein the transparentlayer comprises Al₂O₃, Si, SiC, ZnO, GaAs, GaP, LiAl₂O₃, BN, AN, or GaN.3. The light emitting device of claim 1, wherein the passivation layercomprises SiO₂, MgO, or SiN.
 4. The light emitting device of claim 1,further comprising an additional first metal layer arranged between thefirst metal layer and the p-type bonding pad, wherein the additionalfirst metal layer comprises Ti, Ni, Ag, Zn, Cd, Bi, Cu, Ge, Au, Sn, orPb.
 5. The light emitting device of claim 1, wherein the first metallayer comprises a reflective film.
 6. The light emitting device of claim4, further comprising a second metal layer and an additional secondmetal layer.
 7. The light emitting device of claim 6, wherein the secondmetal layer contacts the n-type nitride semiconductor layer or isadjacent to the p-type nitride semiconductor layer.
 8. The lightemitting device of claim 6, wherein the additional second metal layercomprises Ti, Ni, Ag, Zn, Cd, Bi, Cu, Ge, Au, Sn, or Pb.
 9. The lightemitting device of claim 6, wherein the additional second metal layercomprises an electrode layer.
 10. The light emitting device of claim 1,further comprising: a second nitride semiconductor light emitting cell;and an electrode layer connecting the nitride semiconductor lightemitting cell and the second nitride semiconductor light emitting cellin parallel.
 11. The light emitting device of claim 1, furthercomprising: a second nitride semiconductor light emitting cell; and anelectrode layer connecting the nitride semiconductor light emitting celland the second nitride semiconductor light emitting cell in series. 12.The light emitting device of claim 4, wherein the additional first metallayer is arranged on the n-type nitride semiconductor layer, andconnects the n-type nitride semiconductor layer to the bottom surface ofthe substrate.
 13. The light emitting device of claim 1, furthercomprising a fluorescent substance or a diffusing substance disposed inthe molding member.
 14. The light emitting device of claim 1, furthercomprising a fluorescent substance disposed between the molding memberand the light emitting device.
 15. The light emitting device of claim 1,further comprising a heat sink, wherein the substrate is arranged on theheat sink.
 16. The light emitting device of claim 1, wherein the firstbonding pad is electrically connected to a first metal lead arrangedoutside of a region directly under the light emitting cell.
 17. Thelight emitting device of claim 16, further comprising a second bondingpad connected to a second metal layer.
 18. The light emitting device ofclaim 17, wherein the second bonding pad penetrates through thesubstrate.
 19. The light emitting device of claim 18, wherein the secondbonding pad is electrically connected to a second metal lead, andportions of the first bonding pad and the second bonding pad aredisposed at the bottom surface of the substrate.
 20. The light emittingdevice of claim 1, wherein the molding member comprises a lens shape.